Surface acoustic wave device and filter

Abstract

A surface acoustic wave device includes: comb-shaped electrodes each including electrode fingers and dummy electrode fingers; and additional films located to cover gaps between tips of the electrode fingers of one of the comb-shaped electrodes and tips of the dummy electrode fingers of the other, wherein each of the additional films overlap with at least one of the electrode fingers and the dummy electrode fingers located lateral to the corresponding gap in a first direction in which the electrode fingers extend or in a second direction intersecting with the first direction, and a distance G of the gap is 0<G≤1.0λ and a film thickness h of the additional films is 0<h/λ≤(0.146G+0.694076)×ρ2/ρ1 where λ is a wavelength of an acoustic wave, ρ1 is a density of a material of the additional films, and ρ2 is a density of aluminum oxide.

What is claimed is: 
     
       1. A surface acoustic wave device comprising:
 a pair of comb-shaped electrodes located on a piezoelectric substrate, each of the pair of comb-shaped electrodes including a plurality of electrode fingers and a plurality of dummy electrode fingers, the plurality of electrode fingers of a first comb-shaped electrode of the pair of comb-shaped electrodes and the plurality of dummy electrode fingers of a second comb-shaped electrode of the pair of comb-shaped electrodes being arranged to face each other; and 
 a plurality of additional films, each being located so as to cover a corresponding gap of a plurality of gaps between tips of the plurality of electrode fingers of the first comb-shaped electrode and tips of the plurality of dummy electrode fingers of the second comb-shaped electrode, each of the plurality of additional films covering a single gap among the plurality of gaps, 
 wherein each of the plurality of additional films overlaps with at least a part of at least one of the electrode fingers and the dummy electrode fingers that are located lateral to the corresponding gap in a first direction in which the plurality of electrode fingers extend or in a second direction intersecting with the first direction among the plurality of electrode fingers and the plurality of dummy electrode fingers, and 
 a distance G between the tips of the plurality of electrode fingers of the first comb-shaped electrode and the tips of the plurality of dummy electrode fingers of the second comb-shaped electrode is 0<G≤1.0λ and a film thickness h of the plurality of additional films is 0<h/λ≤(0.146G+0.694076)×ρ2/ρ1 where λ is a wavelength of an acoustic wave excited in the pair of comb-shaped electrodes, ρ1 is a density of a material of the plurality of additional films, and ρ2 is a density of aluminum oxide. 
 
     
     
       2. The surface acoustic wave device according to  claim 1 , wherein
 each of the plurality of additional films overlaps with at least one of the electrode finger and the dummy electrode finger located lateral to the corresponding gap in the first direction, and does not overlap with the electrode finger located lateral to the corresponding gap in the second direction. 
 
     
     
       3. The surface acoustic wave device according to  claim 1 , wherein
 the pair of comb-shaped electrodes are formed of an aluminum film. 
 
     
     
       4. The surface acoustic wave device according to  claim 1 , wherein
 the piezoelectric substrate is a lithium tantalate substrate. 
 
     
     
       5. The surface acoustic wave device according to  claim 1 , wherein
 the plurality of additional films are formed of an aluminum oxide film, a tantalum film, or a silicon oxide film. 
 
     
     
       6. The surface acoustic wave device according to  claim 1 , further comprising:
 a protective film covering the pair of comb-shaped electrodes, 
 wherein the plurality of additional films is located on the protective film. 
 
     
     
       7. A surface acoustic wave device comprising:
 a pair of comb-shaped electrodes located on a piezoelectric substrate, each of the pair of comb-shaped electrodes including a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected, the plurality of electrode fingers of a first comb-shaped electrode of the pair of comb-shaped electrodes and the bus bar of a second comb-shaped electrode of the pair of comb-shaped electrodes being arranged to face each other; and 
 a plurality of additional films, each being located to cover a corresponding gap of a plurality of gaps between tips of the plurality of electrode fingers of the first comb-shaped electrode and the bus bar of the second comb-shaped electrode, 
 wherein each of the plurality of additional films overlaps with at least a part of at least one of the electrode fingers and the bus bar that are located lateral to the corresponding gap in a first direction in which the plurality of electrode fingers extend or in a second direction intersecting with the first direction among the plurality of electrode fingers and the bus bars, and 
 a distance G between the tips of the plurality of electrode fingers of the first comb-shaped electrode and the bus bar of the second comb-shaped electrode is 0<G≤1.0λ and a film thickness h of the plurality of additional films is 0<h/λ≤(0.146G+0.694076)×ρ2/ρ1 where λ is a wavelength of an acoustic wave excited in the pair of comb-shaped electrodes, ρ1 is a density of a material of the plurality of additional films, and ρ2 is a density of aluminum oxide. 
 
     
     
       8. The surface acoustic wave device according to  claim 7 , wherein
 the pair of comb-shaped electrodes are formed of an aluminum film. 
 
     
     
       9. The surface acoustic wave device according to  claim 7 , wherein
 each of the plurality of additional films overlaps with at least one of the electrode finger and the bus bar that are located lateral to the corresponding gap in the first direction, and does not overlap with the electrode finger located lateral to the corresponding gap in the second direction. 
 
     
     
       10. The surface acoustic wave device according to  claim 7 , wherein
 the piezoelectric substrate is a lithium tantalate substrate. 
 
     
     
       11. The surface acoustic wave device according to  claim 7 , wherein
 the plurality of additional films are formed of an aluminum oxide film, a tantalum film, or a silicon oxide film. 
 
     
     
       12. The surface acoustic wave device according to  claim 7 , further comprising:
 a protective film covering the pair of comb-shaped electrodes, 
 wherein the plurality of additional films is located on the protective film. 
 
     
     
       13. A filter comprising:
 a surface acoustic wave device comprising:
 a pair of comb-shaped electrodes located on a piezoelectric substrate, each of the pair of comb-shaped electrodes including a plurality of electrode fingers and a plurality of dummy electrode fingers, the plurality of electrode fingers of a first comb-shaped electrode of the pair of comb-shaped electrodes and the plurality of dummy electrode fingers of a second comb-shaped electrode of the pair of comb-shaped electrodes being arranged to face each other; and 
 a plurality of additional films, each being located so as to cover a corresponding gap of a plurality of gaps between tips of the plurality of electrode fingers of the first comb-shaped electrode and tips of the plurality of dummy electrode fingers of the second comb-shaped electrode, each of the plurality of additional films covering a single gap among the plurality of gaps, 
 wherein each of the plurality of additional films overlaps with at least a part of at least one of the electrode fingers and the dummy electrode fingers that are located lateral to the corresponding gap in a first direction in which the plurality of electrode fingers extend or in a second direction intersecting with the first direction among the plurality of electrode fingers and the plurality of dummy electrode fingers, and 
 a distance G between the tips of the plurality of electrode fingers of the first comb-shaped electrode and the tips of the plurality of dummy electrode fingers of the second comb-shaped electrode is 0<G≤1.0λ and a film thickness h of the plurality of additional films is 0<h/λ≤(0.146G+0.694076)×ρ2/ρ1 where λ is a wavelength of an acoustic wave excited in the pair of comb-shaped electrodes, ρ1 is a density of a material of the plurality of additional films, and ρ2 is a density of aluminum oxide.